This invention relates to an improvement in mounting a load rest on a screw jack.
A general description of a screw jack will suffice to create a setting in which to describe this invention. A conventional screw jack comprises a supporting base, a housing mounted on the base, a gear mechanism within the housing, a load bearing column mounted in the housing to be driven vertically by the gear mechanism, and a drive pinion mounted in the side of the housing to permit a user to drive the gear mechanism to control the height of the load bearing column.
The load bearing column of a screw jack is usually topped with a load rest 1chat can rotate relative to the column to permit convenient positioning of grooves or other locating features on the load rest with respect to surface features of the load. The rotatable load rest assists in maintaining such positioning during lifting or lowering of the column and relative movement of the load. Examples of some load rests of prior art constructions may be found in U.S. Pat. Nos. 1,593,217, 1,600,058 and 5,085,406.
A known type of load rest, to which this invention is directed, has a cap-like structure with a flange that circumferentially surrounds a top portion of the column. The interior of the flange is grooved to receive a fastening mechanism. The column is also adapted to connect to a fastening mechanism. For example, it is known to have dimples spaced about the upper portion of the column which align to the flange groove of the load rest. Ball bearings are inserted into a hole in the flange of the load rest in communication with the flange groove. The load rest is turned to position each successive ball bearing in a dimple until all dimples are filled. When the last ball is placed in a dimple the hole in the flange is plugged. The depth of the dimples is less than the diameter of the ball bearings so that each ball protrudes into the flange groove. The ball bearings then prevent removal of the load rest by interacting with both the groove and dimples.
In another more relevant variation, the column is grooved about its top to align with the load rest flange groove, on assembly. In this configuration it is known to connect the parts with a broken spring wire ring. A ring is compressed in the groove of the column and covered with a sleeve. The load rest is then assembled onto the column to push the sleeve down as it slides over the column groove. When the grooves align the ring springs open into the groove of the load rest. The groove into which the ring is first assembled must have a sufficient depth to completely bury the ring as the load rest is assembled over the column. The other groove will have a depth less than the diameter of the wire to ensure that the ring protrudes from it into the first groove after assembly. Thus the ring fastens tile parts together.
In the competitive environment of manufacture of jacks, particularly vehicle jacks, emphasis is placed on low price, low weight and ease of assembly while maintaining or improving functionality. The ball bearings method described above complicates and slows the assembly procedure, resulting in increased costs of manufacture. The ring method is easy to assemble but the column groove must bury the ring completely during assembly to permit the flange to slip over the column. Column wall thicknesses must accommodate a groove and provide sufficient strength for anticipated loads. The greater wall thickness to bury the; ring increases the weight and material cost of the jack.
It is an object of this invention to provide an improved load rest and column combination that simplifies the construction and reduces the cost of such means while retaining required strength and flexibility. In particular the improvement is directed to the provision of a novel binding ring to permit less intrusive grooves in the column and the load rest. It will be appreciated that this improvement is primarily intended for vehicle jacks but may find application in other screw jacks intended for other end uses.